This invention relates to a coding device and a decoding device used for keeping secrecy of necessary data, and an IC card for storing data necessary for security in coded form, and more particularly to a technique for enhancing reliability in security by coding.
In recent years in Japanese public gamble game shops or Pachinko parlors where pinball machine-like ones are used with steel (Pachinko) balls, prepaid cards are in use when the Pachinko balls or medals are lent to customer players. In order for a customer to borrow the steel balls, the customer has only to put a prepaid card into a reader-writer. The prepaid cards are so convenient for customers because customers do not have to take out coins every time they play that the prepaid cards are nowadays widely in use.
However, the present type of prepaid card is often involved in incidents in which an unauthorized person fraudulently alters the card by rewriting the content data such as kinds of money stored in the card to use it unlawfully. Unlawful use is done on a large scale and enormous amount of damage is inflicted on prepaid card managing companies. In spite of ciphered inside data necessary for security, unfortunate result is that third parties decipher, unlawfully rewrite and alter the data. That is to say, inside data are not ciphered appropriately. Preventing inside data from illegal alteration is also required for magnetic cards and IC cards used as credit cards and cash cards.